The present invention pertains in general to infrared detectors and in particular to such detectors which are responsive to multiple bands of infrared radiation.
Infrared detectors are used for collecting image information under conditions which do not allow generally conventional optical observation, such as at night or through clouds, haze or dust. The information gathered within infrared imaging can be enhanced if multiple bands of infrared radiation can be collected concurrently. This is much like color in an optical image. Infrared radiation in different bands can be indicative of different elements in a scene, such as different materials, reflectivity, temperatures and so forth. Therefore, for optimum viewing through use of infrared radiation, it is desired to have a sensor capable of concurrently detecting multiple bands of infrared radiation.
Multi-band infrared sensing has been performed with detectors of different types. Semiconductor infrared detectors are becoming among the most widely used, and for observing scenes, a well known type is referred to as a xe2x80x9cstaring array.xe2x80x9d One configuration for a multi-band staring array detects each of the different bands of radiation with a planar layer of photosensitive material with the multiple layers in a stack wherein all of the upper layers are transparent to the radiation absorbed by the lower layers.
The present invention is directed to a configuration for an infrared detector which has a unique configuration that is particularly adaptable for use with multi-quantum well (MQW) photosensitive detection material.
A selected embodiment of the present invention is a multi-band quantum well infrared photodetector which has a pixel structure that includes a plurality of co-planar sections, with each section being responsive to a respective, different band of infrared radiation. Each section of the pixel structure has a plurality of elongate, multiple quantum well infrared radiation absorbing elements. Each of the elements has first and second opposite longitudinal surfaces. The elements in each section have a physical configuration which includes a periodic spacing dimension for the elements and a width dimension for the elements. Each of the sections has a respective, different configuration. The multiple quantum well elements comprise a diffraction grating for the infrared radiation. A first contact includes a plurality of planar, electrically interconnected strips respectively in contact with and extending along the first surfaces of the multiple quantum well elements. A plurality of second contacts are respectively located in each of the sections with the second contact in each section electrically connected to the second surfaces of the multiple quantum well elements in the corresponding one of the sections. The first and second contacts are positioned on opposite longitudinal sides of each of said multiple quantum well elements to provide current flow through said elements in a direction substantially transverse to the axis of the elements. A planar reflector is provided for the infrared radiation. The reflector is positioned on an opposite side of the second contacts from the multiple quantum well elements.